1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a transflective LCD device that may selectively use a reflection mode and a transmission mode in a vertical alignment mode LCD device.
2. Discussion of the Related Art
Generally, until recently, cathode ray tubes (CRTs) have been widely used to display image data on a screen, but using CRTs is inconvenient because the CRT tubes are large in size compared to their display areas.
Today, display devices are used in personal computers, notebook computers, wireless terminals, automobile dashboards, and display boards. Also, as a large amounts of image data can be transmitted due to the growth of information telecommunication systems, a next generation display device capable of processing and realizing the large capacity image data is needed.
Next generation display devices should be lightweight and have high brightness, a large screen, low power consumption, and low manufacturing costs. Recently, LCD devices have become attractive as next generation display devices.
The LCD has excellent display resolution compared to other flat display devices and has nearly the same fast response time as that of the CRT that affects image quality when realizing moving images.
The LCD uses the optical anisotropic and dielectric characteristics of liquid crystals. Because the liquid crystals have a thin long structure, the liquid crystals have directionality in their molecular arrangement. Accordingly, the direction of the molecular arrangement can be controlled by applying an electric field to the liquid crystals (molecules).
Therefore, when the molecular direction of the liquid crystals are arbitrarily adjusted, the molecular arrangement of the liquid crystals changes, and light is refracted according to the molecular direction of the liquid crystals by the optical anisotropy, so that an image can be realized.
The twisted nematic (TN) LCD device is one of LCD devices now widely used. The TN LCD device has electrodes on two substrates, respectively, arranges the liquid crystals such that they are twisted by 90°, and applies a voltage to the electrodes to drive the liquid crystals.
Besides the TN LCD device, LCD devices may have a liquid crystal mode using dielectric anisotropy including electrically controllable birefringence (ECB) and a guest-host (GH). The ECB mode uses a negative type liquid crystal (LC) having negative dielectric anisotropy (Δ∈<0) where the LC is oriented in a direction perpendicular to an electric field.
A vertical alignment (VA) mode using ECB modes has a small variation in response time with respect to a gray scale voltage, and thus has an advantage where a response characteristic is excellent compared to the TN LCD device.
In the VA mode LCD device, LCs having negative dielectric anisotropy are interposed between upper and lower substrates, a VA layer is formed on facing surfaces of the upper and lower substrates, and polarizers are attached on backsides of the facing surfaces. At this point, LC driving electrodes are located on the facing surfaces, respectively, and the polarizers are attached such that polarizing axes of the respective polarizers are perpendicular to each other.
In the VA mode LCD device, the LC molecules are arranged vertically with respect to the substrates under the influence of the VA layer. Because the polarizing axes of the upper and lower polarizers are perpendicular to each other, the screen is dark.
Meanwhile, when an electric field is formed between the driving electrodes of the upper and lower substrates, the LC molecules are rotated such that they are perpendicular to a direction of the electric field according to the property of the LCs having the negative dielectric anisotropy. Accordingly, light is transmitted through the LC molecules and the screen becomes white.
Because the LC molecules have an elongated shape, refractive indexes and permittivities along a long axis and a short axis are different from each other. Accordingly, the refractive index varies depending on a direction in which the LC molecules are viewed. Consequently, the displayed image varies as a function of viewing angle.
Therefore, to solve this problem, a pixel electrode of the lower substrate is formed in a slit shape within the pixel so that multiple domains are formed in the pixtel when an electric filed is applied in a related art.
That is, when the electric field is applied between the pixel electrode and a common electrode, anisotropy between the long axis and the short axis of the LC molecule is compensated for by changing the direction of the LC molecule.
However, a multiple domain VA mode LCD device having the above construction may classified into transmissive VA mode LCD devices using a backlight as a light source and reflective VA mode LCD devices using ambient natural light and artificial light without a backlight as a light source.
The transmissive VA mode LCD device realizes a bright image even in a dark external environment using a backlight as a light source. However, the transmissive VA mode LCD device consumes much power.
On the other hand, the reflective VA mode LCD device can reduce power consumption because it does not use a backlight, but cannot be used in dark settings.